The electric machine is provided with a stator, which is preferably arranged in a stationary manner in a machine housing of the electric machine. On the other hand, the rotor is rotatably mounted with respect to the stator and thus also with respect to the machine housing. For example, the rotor is rotatably mounted on and/or in the machine housing, in particular by means of a bearing, preferably a roller bearing. The rotor is in this case arranged on a coolable shaft. This is to be understood so that the rotor and the shaft are formed separately from each other and joined together subsequently. However, it can be also provided that the shaft is formed integrally with the rotor.
The shaft and therefore also the rotor are arranged in the longitudinal section with respect to an axis of rotation of the shaft, preferably at least in some regions within the stator. For example, the shaft completely engages the stator in the axial direction with respect to the axis of rotation, which is to say that it projects axially beyond the latter, seen in the axial direction.
The shaft is coolable. This means at least that the shaft consists of a heat-conducting material so that the heat supplied to the shaft is dissipated by means of the heat conduction. However, the shaft can be also coolable actively, for which purpose a corresponding cooling device is associated with it. Such a cooling device can be for example a hollow shaft and/or lance cooling.
In the first case, at least one coolant channel is formed in the shaft, through which a coolant can flow. The shaft can be designed for example as a hollow shaft.
Additionally or as an alternative, lance cooling can be provided. Also in this case, the shaft is provided as a hollow shaft, at least in some sections. In this case, a cooling lance is engaged in the shaft, for example by means of an opening formed in the shaft on the front face side. A coolant is introduced by means of the cooling lance into the shaft, in particular injected into it. In both cases, the coolant absorbs the heat supplied to the shaft and conducts it away from the shaft.
The electric machine can be designed for example as an asynchronous machine or as a synchronous machine that is excited by current. The continuous power concentration, which is to say the continuous power that the electric machine can provide at a specified weight and/or volume, is primarily limited thermally. In the case of electric machines having rotor-critical characteristics, the heat dissipation from the rotor is in particular of decisive importance for the permanent line density to be achieved. For example, the heat generated in or at the rotor is dissipated by the shaft in the described manner, in particular via the coolable or actively cooled shaft. Additionally or as an alternative, recirculated air cooling is also possible.